1. Field of the Invention
The present invention relates to a wheel with a spring unit for a vehicle.
2. Description of Related Art
A wheel including a rim, a disc and an elastic member connecting the rim and the disc is known. The wheel with the elastic member decreases a road noise of the vehicle, when for the elastic member, a rubber, a leaf spring having a wave, and a plurality of radially directed coil springs are used.
The wheel with the elastic member requires a spring force generating a radial force and a circumferential force for obtaining the aimed characteristic. The disc is biased toward a center of the rim by the radial spring force. The radial spring of the elastic member and a mass of the rim constitute a dynamic damper which decreases a road noise. The circumferential spring force transmits a drive and brake force between the disc and the rim.
The conventional wheel with the damper has the following A-F problems:
(A) The Distance Between the Rim and the Disc is Large.
{circle around (1)} Rubber-Type Elastic Member
The wheel with the elastic member obtains a necessary elastic force by the rubber. The spring constant of the rubber is determined so as to decrease a road noise at the vicinity of 100 Hz. When a vehicle load is imposed on the wheel, a large displacement is generated between the rim and the disc at an upper portion and a lower portion of the wheel. When the spring constant of the rubber is determined so as to decrease the road noise, the clearance between the rim and the disc is about 25 mm.
{circle around (2)} Leaf Spring-Type Elastic Member
The leaf spring is fixed to the rim and the disc not by welding but by a rivet so as to prevent the spring from losing its elasticity due to heat of welding and to relax stress concentration which may be generated if the spring is fixedly coupled to the rim and the disc. The leaf spring may be coupled to the rim and the disc via metal retainers. As a result, a space for disposing the metal retainers is necessary. Further, a space for rivet-working is necessary between the inside and outside retainers. Furthermore, since the leaf spring deforms in a radial direction of the wheel also, it is necessary to provide a clearance for the deformation. Summing up these clearances, a necessary clearance between the rim and the disc is about 25 mm or more.
{circle around (3)} Other Spring-Type Elastic Member (Where an Axis of the Spring is Directed in a Radial Direction of the Wheel)
When the other-type spring is used with its axis directed in the radial direction of the wheel, a relatively large space is necessary to be provided between the rim and the disc in order to obtain a necessary durability of the spring. The necessary space is about 40 mm or more.
(B) The Reliability of the Elastic Member is Insufficient.
{circle around (1)} Rubber-Type Elastic Member
Consideration has to be taken to the durability because the durability of the rubber-type elastic member is affected by ultraviolet rays, ozone, salt, etc.
{circle around (2)} Leaf Spring-Type Elastic Member
The leaf spring is twisted and plastically deformed receiving an excessively large lateral force and the spring characteristic becomes unstable. When twisted, a large local stress concentration will be generated in the leaf spring and the spring is likely to be broken. However, there are few examples used for the wheels, consideration of which is necessary.
(C) There is no Fail-Safe Mechanism in a Rotational Direction.
When the rubber member is broken, there is no engagement between the rim and the disc, and no drive and brake torque is transmitted between the rim and the disc.
(D) Cost is High.
{circle around (1)} Rubber-Type Elastic Member
Equipment for conducting vulcanizing-adhesion is high in cost, and the time for conducting vulcanizing-adhesion is long.
{circle around (2)} Leaf Spring-Type Elastic Member
A large retainer and a special spring are needed. Further, a relatively long time period is necessary for mounting the spring to the wheel. Therefore, the cost is high.
(E) Stability and Controllability are Relatively Low.
{circle around (1)} Rubber-Type Elastic Member
In a large amount of steering, since the rigidity of the elastic member is low in the steering direction, the steering force is absorbed at the elastic member and therefore, the tire cannot be steered by the same amount as the steering handle is rotated.
If the steering rigidity of the rear wheel is low, the rear wheel is steered in an opposite direction when the vehicle is turned, and the vehicle is over-steered.
In a small amount of quick steering, the steering is delayed due to a hysteresis generated by an internal friction of the rubber.
{circle around (2)} Leaf Spring-Type Elastic Member
The rigidity of the leaf spring is high in the steering direction so long as a width of the leaf spring is large. However, cost is high.
(F) Regarding a Harmful Noise
{circle around (1)} Leaf Spring-Type Elastic Member
Since the leaf spring is coupled to the rim and the disc by a rivet, a slippage happens at the rivet portion to cause a metal slippage noise.
{circle around (2)} Other Spring-Type Elastic Member
In a case where an end of the spring directly contacts the rim and the disc, a noise is likely to be created. To suppress the noise, a retainer for receiving the end of the spring will be necessary, and the cost therefore will be high.